1. Field of the Invention
The present invention relates to an ink-jet recording head provided with pressure generators that produce pressure in pressure chambers, respectively to jet ink.
2. Description of the Related Art
A conventional ink-jet recording head (hereinafter, referred to simply as xe2x80x9crecording headxe2x80x9d) provided with piezoelectric vibrators of a flexural vibration mode will be described by way of example with reference to FIGS. 7 to 9. As shown in FIGS. 7 to 9, the recording head has actuator units 100 and a passage unit 105 superposed on the actuator units 100.
Each actuator unit 100 includes a pressure chamber forming plate 10 provided with a plurality pressure chambers 2, a vibrating plate 11 superposed on the pressure chamber plate 10 so as to cover the open upper ends of the pressure chambers 2, and a plurality of piezoelectric vibrators 6 placed at positions respectively corresponding to the plurality of pressure chambers 2 on the vibrating plate 11.
The passage unit 105 includes a nozzle plate 17 provided with nozzle apertures 3, a storage chamber forming plate 16 provided with ink storage chambers 4, and an ink supply port forming plate 18 superposed on the storage chamber forming plate 16. The passage unit 105 is attached to the lower surface of the actuator units 100. Each pressure chamber 2 is an elongated slot having one end communicating with the ink storage chamber 4 and the other end communicating the nozzle aperture 3.
The ink storage chamber forming plate 16 is provided with connecting holes 9 communicating with the nozzle apertures 3. The ink supply port forming plate 18 is provided with ink supply ports 15 through which the ink is supplied from the ink storage chambers 4 into the pressure chambers 2, and connecting holes 8 connecting the pressure chambers 2 and the connecting holes 9 communicating with the nozzle apertures 3, respectively. The ink supply port forming plate 18 is provided also with ink supply ports 24 through which the ink is supplied from an ink cartridge, not shown, into the ink storage chambers 4.
The recording head shown in FIG. 7 is a six-color recording head that prints in six color inks. The recording head is provided with the three actuator units 100. Each actuator unit 100 is provided with two rows of the pressure chambers 2 arranged in a feed direction in which a recording sheet is fed. The three actuator units 100 are arranged in a scanning direction along the width of the recording sheet in which the recording head is moved for printing. The six ink storage chambers 4 of the passage unit 105 are arranged along the width of the recording sheet so as to correspond to the rows of the pressure chambers 2, respectively. The color inks of the different colors are jetted through the nozzle apertures 3 of the six rows respectively corresponding to the rows of the pressure chambers 2.
Lower electrodes 19 are formed on the upper surfaces of portions of the vibrating plate 11 of each actuator unit 100 corresponding to the pressure chambers 2, respectively. Flat piezoelectric vibrators 6 are formed on the upper surfaces of the lower electrodes 19 and an upper electrode 20 is formed on the upper surfaces of the piezoelectric vibrators 6, respectively.
As shown in FIG. 8, terminals 21 are formed on the opposite ends of the upper surface of each actuator unit 100 so as to be connected electrically to the upper electrodes 20 on the piezoelectric electric vibrators 6, respectively. A flexible wiring board 22 is placed on the terminals 21. Driving signals are applied through the terminals 21 and the upper electrodes 20 to the piezoelectric vibrators 6.
The ink drops are jetted through the nozzle apertures 3 by producing pressure in the pressure chambers 2 by the flexural vibration of the piezoelectric vibrators 6. As shown in FIG. 10, the piezoelectric vibrator 6 contracts laterally when a driving signal is applied to the piezoelectric vibrator 6. A lower portion of the piezoelectric vibrator 6 fixed to the vibrating plate 11 does not contract and only an upper portion of the same contracts. Consequently, a portion of the vibrating plate 11 corresponding to the piezoelectric vibrator 6 and the piezoelectric vibrator 6 bend in a downward convex shape to compress the pressure chamber 2, so that the pressure in the pressure chamber 2 is increased and the ink contained in the pressure chamber 2 is jetted through the nozzle aperture 3 in the form of an ink drop 23. The ink drop 23 forms a dot on the recording sheet for printing. When the driving signal is removed from the piezoelectric vibrator 6 to allow the piezoelectric vibrator 6 to return to its original shape, the ink is supplied from the ink storage chamber 4 through the ink supply port 15 into the pressure chamber 2.
In the conventional recording head, the six ink storage chambers 4 are formed in the single storage chamber forming plate 16 to supply the inks from the six ink storage chambers 4 to the six rows of the pressure chambers 2 and the inks are jetted through the six rows of the nozzle apertures 3. Since the six ink storage chambers 4 are arranged laterally in a plane, the recording head necessarily has a large lateral size.
Studies have been made in recent years to use more than six color inks for the further improvement of print quality. The use of more than six color inks inevitably entails increase in the size of the recording head, affects adversely to accuracy and hence has not been realized.
In another known recording head, one row of pressure chambers 2 is divided into a plurality of sections, and a plurality of ink storage chambers 4 are formed for the sections of the row of the pressure chambers 2, respectively, to use a plurality of color inks. This known recording head, similarly to the foregoing conventional recording head, needs one storage chamber forming plate provided with many ink storage chambers 4 and there is a limit to the reduction of the size of the recording head.
The present invention has been made in view of the foregoing problems and it is therefore an object of the present invention to provide an ink-jet recording head of a small size and capable of using an increased number of kinds of inks without increasing the size.
According to the present invention, an ink-jet recording head has: an actuator unit including a pressure chamber forming plate provided with a plurality of pressure chambers, and a plurality of pressure generators that produce pressure in the pressure chambers, respectively, to jet ink, the pressure chambers being grouped into two or more pressure chamber groups that correspond to two or more kinds of inks, respectively; and a passage unit stacked on the actuator unit and including two or more ink storage chamber forming plates that are stacked on each other, each of the two or more ink storage chamber forming plates being provided with at least one ink storage chamber, the ink storage chambers storing inks to be supplied to the pressure chamber groups, respectively.
Preferably, the pressure chambers are arranged in a row. The passage unit may have two or more ink inlet openings through which inks are supplied into the two or more ink storage chambers, respectively. The two or more ink inlet openings may be arranged in a direction perpendicular to a direction in which the pressure chambers are arranged.
Preferably, the ink-jet recording head further has at least one partition plate interposed between the storage chamber forming plates. The two or more ink storage chambers may overlap at least partly each other with respect to a direction in which the two or more storage chamber forming plates are stacked. Portions of the two or more ink storage chambers overlapping each other may be isolated from each other by the partition plate.
Preferably, the partition plate is a flexible plate capable of being distorted by pressure applied to the pressure chamber.
Preferably, the ink storage chambers of the passage unit have profiles that are formed of smooth curves.
Preferably, the pressure chambers that receive ink from the same ink storage chamber are arranged adjacently.
Preferably, the pressure generators are piezoelectric vibrators of a flexural vibration mode.
Preferably, the pressure generator applies pressure to the pressure chamber in a direction in which ink is jetted.